This invention relates to a surface acoustic wave device with a novel structure that yields excellent performance.
As structures of surface acoustic wave devices (substrates) to deal with various electrical signals there are conventionally known the following:
1. a single structure consisting of only a piezoelectric substrate (piezoelectric single-crystal substrate, piezoelectric ceramic substrate, etc.); PA1 2. a laminated structure with a piezoelectric film being deposited on a non-piezoelectric substrate;
3. a laminated structure with a piezoelectric film being deposited on a semiconductive substrate; and others.
A known format of the laminated structure of No. 2 in the above comprises a sapphire substrate or a glass substrate with a zinc oxide film (ZnO) deposited thereon by sputtering. However, zinc oxide film has the following drawbacks:
1. it is difficult to obtain good quality of film, thereby causing fabrication of devices inferior in piezoelectricity, etc.;
2. propagation loss of surface acoustic wave is large in the high frequency range;
3. dispersion propagation characteristics of a surface acoustic wave is large; and
4. it is difficult to control variation ratio (1/.tau.).multidot.(.differential..tau./.differential.T) of delay time (.tau.) of surface acoustic wave depending on variation of temperature (T is ambient temperature).